[new release] mirage-nat (2.2.4)
[new release] mirage-nat (2.2.4)

CHANGES:

- avoid deprecated Cstruct.len, use Cstruct.length (mirage/mirage-nat#45 @hannesm)
- remove rresult dependency (mirage/mirage-nat#45 @hannesm)
- raise lower OCaml version to 4.08.0 (mirage/mirage-nat#45 @hannesm)
- remove stdlib-shims dependency (mirage/mirage-nat#45 @hannesm)

djs55/opam-repository,c-cube/opam-repository,pirbo/opam-repository,Leonidas-from-XIV/opam-repository,c-cube/opam-repository,toots/opam-repository,pqwy/opam-repository,jhwoodyatt/opam-repository,jhwoodyatt/opam-repository,ocaml/opam-repository,codinuum/opam-repository,Leonidas-from-XIV/opam-repository,hannesm/opam-repository,djs55/opam-repository,andersfugmann/opam-repository,yallop/opam-repository,kkirstein/opam-repository,emillon/opam-repository,yallop/opam-repository,nberth/opam-repository,Chris00/opam-repository,astrada/opam-repository,hannesm/opam-repository,pirbo/opam-repository,astrada/opam-repository,toots/opam-repository,nberth/opam-repository,ocaml/opam-repository,kkirstein/opam-repository,emillon/opam-repository,Chris00/opam-repository,fpottier/opam-repository,mjambon/opam-repository,fpottier/opam-repository,andersfugmann/opam-repository,pqwy/opam-repository,mjambon/opam-repository,codinuum/opam-repository